The present invention relates to data storage devices and control methods for the same, and more particularly, to a data storage device preventing unexpected movement of an access unit which accesses a storage medium, and a method of controlling this storage device.
Devices known as data storage devices use various types of media such as an optical disk or magnetic tape. Among these storage devices is a hard-disk drive (HDD) most commonly used as a storage device in a computer, and the HDD is one of storage devices indispensable in current computer systems. Furthermore, the excellent characteristics of the HDD are increasingly expanding its applications not merely as an element of a computer, but also as a removable memory in a product such as a dynamic-image recording/reproducing device, car navigation system, or digital camera.
The magnetic disk used for the HDD has a plurality of concentrically formed tracks, and address information (servo information) and user data are stored into each of the tracks. Magnetic heads each formed of thin-film elements can write in or read out data by accessing a desired region (address) in accordance with address information. The signals that a magnetic head has read out from the magnetic disk during a data readout process are provided with waveform shaping, decoding, and other required signal processing, by a signal-processing circuit, and then transmitted to a host. After undergoing required processing by the signal-processing circuit similarly to the above, transfer data from the host is written onto the magnetic disk.
The magnetic head is fixed to a slider, and the slider is further fixed to a turnable carriage. The carriage is oscillated by a voice coil motor (VCM) to allow the magnetic head to be moved to a desired position on the magnetic disk. The VCM is driven by a VCM driver, which drives the VCM by supplying a current thereto in response to the control data sent from a controller.
As described above, each track includes a data region into which data is stored, and a servo region into which servo information is stored. A cylinder ID, a servo sector number, a burst pattern, and other data are stored as servo data into the servo region. The cylinder ID, which denotes a track number, and the servo ID, identify track and servo sector addresses, respectively. The burst pattern includes relative position information of the magnetic head with respect to the track. The burst pattern is constructed of a plurality of signal storage region arrays different from one another in terms of the phase of a signal storage region; each region being adapted so that signals are stored thereinto, and being disposed with a fixed spacing in the radial direction of the disk.
Data reading from or writing onto the magnetic disk is accomplished while the position of the corresponding magnetic head is being confirmed by means of servo information under the rotating state of the magnetic disk. Servo information that has been read by the magnetic head undergoes arithmetic processing by the controller. The value of the current to be supplied to the VCM is determined by being calculated from the relationship between the current position of the magnetic head and the intended position thereof. The controller generates the control data DACOUT that indicates the above-calculated electric current value, and supplies the current to the VCM driver. In case of a deviation, the carriage is driven to compensate for the deviation, whereby the position of the magnetic head is controlled.
Movement of the magnetic head, however, may become uncontrollable for reasons such as a servo information error, noise current, servo logic circuit fault, or software bug. In such a case, the magnetic head may enter the so-called “runaway” condition, and if this actually happens, the magnetic head or the slider will collide and suffer damage.
Japanese Patent Laid-open No. 2003-059216 discloses one method for solving the above problem. A speed control value generated on the basis of servo information is converted into an analog signal (voltage signal) by a digital/analog converter (D/A converter) and then further converted into a driving current for the VCM. The VCM is driven by this driving current. The speed control value for setting the moving speed of an actuator, namely, the magnetic head, is generated and output at the required intervals on the basis of the servo information. If the magnetic head is under a runaway state, however, the speed control value is not generated at the required intervals. Accordingly, the generation of the speed control value is monitored and if it is not generated at the required intervals, the magnetic head is regarded as not under a runaway state, and a measure is taken to protect the magnetic head from runaway.